1. Field of the Invention
The present invention relates to an a liquid crystal display (LCD) device and color adjustment thereof, and more particularly, to an LCD device having a plurality of lamps of different color coordinates for color adjustment and a color adjustment method.
2. Description of the Related Art
In general, there are various ways to display information using devices such as cathode ray tubes, utilizing light emission of thermions impacting a fluorescent substance, LCDs, plasma display panels, etc. Among those devices, the LCD device is currently widely used due to its many advantages such as that power consumption is low compared to other display devices, manufacture of diverse sizes is possible, a display pattern can be formed in many ways, low voltage operation is possible, and an interface with large scale integrated complementary metal oxide semiconductor circuits is very easy.
However, since the common LCD device is a light-reflecting light-emission device which forms an image by reflecting external light rather than by emitting light by itself, the image can not be viewed in a dark place. Thus, an illumination apparatus must be installed at the rear surface of the LCD device so that the image can be viewed in a dark place.
As the illumination lamp for the back light of the LCD device, a point light source such as a glow lamp, or a white light halogen lamp, a linear light source such as a fluorescent lamp (hot cathode or cold cathode), or a plane light source such as light emitting diodes in a matrix format may be used. The fluorescent lamp has mercury and rare gas sealed in a lamp. When the lamp discharges, the mercury emits ultraviolet rays which collide with a fluorescent substance coating the inside surface of the lamp tube, to emit visible light. The rare gas is mostly argon gas and the sealing is to control the speed of electrons during discharge and restrict sputtering of electrodes.
Back lights for LCD devices can be divided into edge types and downside types according to the arrangement of a light source. In the edge type, a fluorescent lamp, which is a linear light source, is arranged at the edge of a display surface, whereas in the downside type, one or a plurality of light sources are arranged underneath of the display surface.
FIGS. 1A and 1B are exploded perspective views of an LCD device having back lights of the downside type and edge type, respectively.
FIG. 1A shows a the to the downside type back light used when a high brightness is required as in a color LCD television. An LCD panel 13 has substrates facing each other and on which an electrode having a strip shape is formed. And liquid crystal fills the space between the substrates. A lamp 11 is disposed below the LCD panel 13 and light falling on a surface of the LCD panel 13 is made uniform by using a reflection plate 14 and a diffuser plate 15. The light generated from the lamp 11 is reflected by the reflection plate 14, diffused by the diffuser plate 15, and selectively transmitted through the LCD panel 13. An inverter 16 provides a voltage for illuminating the lamp 11.
FIG. 1B shows an edge type back light when uniformity of light is more valued than brightness. A lamp 14 is disposed at the edge of the LCD panel 13 and the light generated by the lamp 14 indirectly reaches the LCD panel 13 through a light transmitting plate 12 such as an acrylic resin. Here, the effect of the light transmitting plate 12 can be improved by attaching a diffuser plate and a reflection plate (not shown) on the upper and lower surfaces of the light transmitting plate 12. An inverter 16 provides a voltage for illuminating the lamp 11.
A color LCD device has a color filter. The color filter can be manufactured integrally with the LCD panel 13 shown in FIGS. 1A and 1B. The color filter is composed of pixels, each of which has filter elements of red (R), green (G), and blue (B) colors to transmit light of a particular wavelength range from the light of the back light passing through the liquid crystal cell. The liquid crystal in the liquid crystal cell is tilted at a predetermined angle by the application of a liquid crystal driving voltage. The light of the back light passes through one of the R, G, and B color filters according to the tilting of the crystal liquid, while passing through the liquid crystal cell. Light passing through the filter generates light of one color at each pixel, so that a plurality of pixels together embody color.
FIG. 2 is a graph showing relative light intensity of a fluorescent lamp for a back light and a color filter with respect to light transmission wavelength.
When light emitted from the fluorescent lamp back light is split, a wavelength peak occurs in an area corresponding to a wavelength range of a particular area which is selectively transmitted in the color filter. That is, a common fluorescent lamp for a back light is manufactured by coating with a fluorescent substance which is made by blending three sorts of rare-earth elements respectively emitting red (R), green (G), and blue (B). The light emitted from such a fluorescent lamp is white as a whole. The white light generated from the fluorescent lamp is selectively transmitted through the color filter so as to emit light of an arbitrary color. Here, if the white light is split, there occur a couple of peaks with respect to relative light intensity in the entire wavelength distribution which is coincident with a transmission area of the light transmitted by the R, G, and B filters formed on the color filter. Namely, as shown in FIG. 2, the peaks of light generated from the fluorescent lamp are at about 450 nm, 540 nm, and 610 nm, respectively, which correspond to the light transmission areas for the R, G and B colors. The areas where the peaks are formed in the wavelength distribution of the fluorescent lamp can be arbitrarily altered during manufacture of the fluorescent lamp.
According to the conventional technology, in order to adjust the color displayed in the LCD device, a fluorescent lamp having the desired color is installed. That is, by selecting the fluorescent substance coating the fluorescent lamp, a different lamp having altered peaks in the wavelength distribution is adopted as a back light. For instance, when an LCD device exhibiting a superior reemergence of blue color is to be manufactured, there is no alternative to installing a fluorescent lamp back light having a greater peak value in the wavelength distribution, particularly in the transmission wavelength area of a blue filter. However, since this method is performed only in the manufacturing process of the LCD device, there is no chance to involve a user. That is, a user can not arbitrarily adjust the color of the LCD device, so it is not possible to adjust the color to adapt to a change of circumstances while using the LCD device.